Microwave rectifiers



Nov. 23, 1965 J. M. OSEPCHUK MICROWAVE RECTIFIERS Filed Dec. 22, 1960 n 4 /X ///4 J/ /(/////J SOURCE LOAD I NVERTER RF SOURCE F/G. 2b

//VVEA /TOR JOHN M. OSEPCHUK ATTORNEY.

United States Patent 3,219,904 MICROWAVE REOTIFIERS John M. Osepciaulr, Lexington, Mass, assignor to Raytheon Company, Waltham, Mass, a corporation of Delaware Filed Dec. 22, 1960, Ser. No. 77,664 9 Claims. (Cl. 321-8) This invention relates to microwave rectifiers and more particularly to a traveling wave device for converting microwave power to direct current power.

The efiicient conversion of microwave power to direct current power has long been a problem to those working in the microwave field. At present, semiconductors such as point contact silicon diodes and a few other types of semiconductors have been found suitable for detecting high radio frequency (RF) or microwave signals. However, the efficiency of the rectification involved is, as a rule, quite low, and the semiconductors are incapable of rectifying substantial amounts of power. it is one object of the present invention to provide a device for converting microwave power to D.C. power operating at at least 30 to 40 percent eificiency and capable of converting hundreds of watts of microwave power to direct current power or low frequency (Le. 60 cycle) power employing a traveling wave type electron discharge device.

In the present invention microwave power is applied to a slow wave propagating structure or delay line which is coupled in energy exchanging relationship with electrons issuing from a cathode, the potential of the latter being positive with respect to the delay line. As the wave propagated in the line gives up energy to the electrons, the electrons move closer and closer to the delay line and eventually are collected by the line as direct current (D.C.) yielding D.C. power to some load. The velocity synchronism between the wave and the electrons may be as in either a forward or backward wave type traveling wave device.

Electrons forming the beam are compelled to travel through an interaction space adjacent the delay line by crossed electric and magnetic fields. The electric field in the space is bounded by the delay line and an elongated electrode (sole electrode) coextensive therewith, the delay line being preferably maintained at a potential negative with respect to the elongated electrode. As power is transferred from the wave to the electrons, the electrons, being negative, move to lower and lower electrostatic equipotential lines in the interaction space between the delay line and the elongated electrode, thus moving closer and closer to the delay line as they absorb more energy from the waves. Eventually, electrons strike the delay line and are collected there. A D.C. load coupled between the delay line and the cathode in the tube serve to dissipate this D.C. current flow to the line, and in addition, raise the potential of the cathode depending on the impedance of the load and the D.C. current of electron flow to the line. The applicant has discovered that operation of such a device with forward wave interaction and with the delay line negative with respect to the elongated sole electrode results in superior operation. By maintaining the delay line substantially more negative than the sole electrode and also more negative than the cathode, sorting of the electron beam is practically eliminated, and the device will neither oscillate, if interaction is in a backward mode, nor amplify, if interaction is in a forward mode, but will convert microwave power to D.C. power. Under such conditions of operation most of the electron current is collected by the delay line and only a small portion is collected by the sole electrode or other electrodes.

Various embodiments of the invention disclose applications of the microwave rectifier wherein a part of the D.C. power output is employed to energize a power supply for applying voltages to the electrodes in the device.

Other features and objects of the invention will be more apparent from the following specific description taken in conjunction with the drawings in which:

FIG. 1 illustrates a crossed-field traveling wave structure for converting microwave power to D.C. power;

FIGS. 2a and 2b illustrate electron paths to show at least one advantage for employing a negative rather than a positive potential delay line; and

FIG. 3 illustrates an embodiment of the invention wherein a portion of the output power energizes a power supply applying voltages to the electrodes in the tube.

Turning first to FIG. 1 there is shown a crossed-field traveling wave structure device 1 including a suitable delay line 2 which is electrically connected to the conductive envelope 3 of the device, a cathode 5 located at one end of the delay line consisting of an electron emissive surface 6 and a support 7 carrying electrically conductive leads to the surface and to a heater element (not shown) for heating the surface causing it to emit electrons which forms a beam. An elongated sole electrode 8 substantially coextensive with the delay line 2 forms an interaction space 9 with the delay line through which the electrons are compelled to travel and is supported by insulated terminal 10 which carries a lead to an external potential source 11. An accelerating electrode 12 is disposed opposite the emissive surface 6 and supported by an insulated terminal 13 through which a potential is applied to electrode 12 from potential source 11.

A magnetic field B indicated by circles 14 is applied substantially perpendicular to the electric field in interaction space 9 and the electric field running from electrode 12 to cathode 5. The crossed electric and magnetic fields compel electrons from emissive surface 6 to travel arcuate paths entering interaction space 9 along a given electrostatic equipotential line and generally proceed along shallow cycloidal paths or substantially rectilinear paths from one end of the space to the other. Microwave or RF power is applied to delay line 2 from source 15 via insulated terminals 16 and 17. As these electrons gain energy from the RF wave propagated in delay line 2 they move to lower and lower equipotential lines and, thus, move closer and closer to the delay line. Electrons entering the interaction space in proper phase with the RF wave will eventually impinge upon the delay line as shown by the part of the beam denoted 18. Other electrons of different phase with the RF wave will not be collected by the delay line but will fall upon a collector electrode 19 supported at the other end of the interaction space by insulated terminal 20 through which a potential is applied to the collector electrode from potential source 11. These unfavorably phased electrons are denoted by beam 21. Other electrons of unfavorable phase will follow paths denoted 22 and strike the sole electrode 3.

Generally speaking the above operation is the same whether RF power is fed to the delay line 2 in the direction of arrow 23 for forward wave interaction or in a direction of arrow 24 for backward wave interaction. Since electrons are emitted from cathode surface 6 at the potential of source 11 and the vast majority of the electrons are collected by delay line 2 at ground potential, the potential at junction 25 will swing positive and, accordingly, the potentials at cathode surface 6, sole electrode 3, accelerating electrode 12 and collector electrode 19 will swing more positive. The greater the electron current from emitting surface 6 to delay line 2, the more positive will be the swing of the cathode. As a result, D.C. current will be applied from the cathode to load 26 which is coupled at one end to delay line 2 and to ground. A typical operation, for example, converts about 200 watts 3 of S band frequency signal (2300 mc.) from source 15 to at least 160 watts in a K load 26.

The embodiment shown in FIG. 1 includes an accelerating electrode 12 at a higher potential than the cathode 5, but at lower potential than sole electrode 8, thus electric field strength in the space between cathode 6 and electrode 12 at the commencement of operation is lower than in the interaction space 9 between sole electrode 3 and delay line 2. While this condition may be preferred in some embodiments, it is not preferred in all. In some applications, electrode 12 may be an extension of the sole electrode and at the same potential, thus producing a substantially uniform strength electric field throughout at the commencement of operation. However,

subsequently, in such applications, when cathode potential rises with respect to the delay line, a greater electric field strength exists in the interaction space 9.

One advantage to be gained by employing a negative voltage delay line as shown in FIG. 1 is that less dissipation from striking electrons will result for a given microwave power input level. Such delay line dissipation represents a loss in power and efficiency. If the electron beam has a perfectly rectilinear trajectory as shown by trajectories A in FIGS. 2a and 2b, then the electrons will simply drift slowly toward the delay line, and little dissipation will result when they strike the delay line. FIG. 2a illustrates the trajectory of electrons in an interaction space between a sole 27 and a delay line 28 where the delay line is at a positive DC. potential relative to the sole, while FIG. 2b illustrates trajectories where the delay line is negative DC. potential relative to the sole. If, however, the trajectories are not perfectly rectilinear, but are cycloidal, as illustrated by trajectories B then electron bombardment energy is a maximum in the case where the line is positive and is a minimum in the case where the line is negative with respect to the sole. As shown in FIG. 2a, electrons following a cycloidal path B will strike the sole at the peak of the path where electron velocity is at a maximum. On the other hand, if the delay line is at a nega tive potential as shown in FIG. 2b, electrons will impinge upon the line at the bottom of the cycloidal trajectory Where electron velocity is at a minimum. This indicates that the cycloidal trajectory is desirable in the negative delay line 2 and is, in fact, preferred to rectilinear trajectories for the purpose of minimum delay line dissipation.

Electron trajectories can be made substantially rectilinear or substantially cycloidal by suitable variations of potentials applied to electrodes and/or by maintaining a suitable ratio of electric field to crossed magnetic field strength in the interaction space.

FIG. 3 illustrates a useful embodiment whereby the required biases for any or all of the electrodes 8, 12 and 19 are obtained from the microwave rectifier itself. As shown in FIG. 3, RF power is applied to delay line 2 from RF source and potentials from power supply 29 are applied to cathode 6 and electrodes 8, l2 and 19 by suitable leads coupled thereto. The electron flow from cathode 6 to line 2 will cause a rise in the potential of cathode 6 and a corresponding rise in the potentials applied to electrodes 8, 12 and 19. Cathode 6 is coupled to ground through a power divider 30 and a load 31, thus providing useful DC. power to the load. Power divider 30 serves to extract a small amount of power from the total useful DC. power, and this small amount of power is applied to inverter 32 which converts DC. to a suitable 60 or 400 cycle signal for energizing power supply 29 through transformer 33. As a result, all power energizing the complete system shown in FIG. 3 is derived from the applied RF source.

A plurality of microwave power rectifiers such as shown in FIG. 1 can be employed in such a manner that the exhaust microwave power carried by the return line to source 15 feeding power to a relatively high power microwave rectifier, could be applied to a second similar rectifier which provides DC. power ,to a power supply. The output of the power supply would serve to' provide potentials for energizing electrodes in the high power rectifier. For example, a low power rectifier can be operated as shown in FIG. 3 except that all DC. power from cathode 6 would be applied directly to the inverter 32, but only a small fraction of the power from source 15 Would be applied to the delay line 2. Power supply 29 would serve to energize electrodes of this low power rectifier just as shown in FIG. 3 and also to energize electrodes in a high power rectifier (not shown) which converts the greater part of the power from microwave source 15 to DO.

Other combinations of microwave power converters such as disclosed herein will yield increased efficiency of rectification depending on problems encountered, and it should be clearly understood that structures disclosed herein are made only by way of example and do not limit the spirit and scope of the invention. For example, it is apparent that a helical type delay line or an interdigital type line might be employed for slow propagation of the microwave which interacts with an electron beam imparting energy to the beam causing beam electrons to move to lower equipotential lines for collection by the delay line or another electrode so that a DC. load coupled to the cathode may be energized. Furthermore, other methods for increasing the etficiency of the device may make use of some or all of the DC. output power to energize electrodes therein without deviating from the spirit or scope of the invention as set forth in the accompanying claims.

What is claimed is:

1. An electron discharge device comprising a slow wave propagating structure biased at a negative DC. potential coupled to a source of alternating microwave frequency signals, means emitting electrons at a higher negative potential than said slow wave structure potential, means compelling said electrons to travel in energy exchanging relationship with waves propagated in said structure and a DC). load coupled between said emitting means and said structure whereby power from said source of alternating signal is converted to DC. power applied to said load.

2. An electron discharge device comprising a delay line coupled to a source of RF signal and biased at a negative D.C. potential, means emitting electrons at a DC. potential more highly negative than said delay line potential, means compelling said electrons to travel in energy exchanging relationship with waves propagated in said delay line and a DC. load coupled between said means emitting electrons and said delay line whereby power from said source of RF signal is converted to DC. power applied to said load.

3. An electron discharge device including a slow wave propagating structure biased at a negative D.C. potential coupled to a source of RF signal, means emitting electrons at a substantially higher negative potential than said structure, means compelling said electrons to travel in energy exchanging relationship with waves of said RF signal propagated in said structure thereby extracting energy from said waves and impinging upon said structure, and a DC. load coupled between said emitting means and said structure whereby RF power from said source is converted to DC. power in said load.

4. An electron discharge device including a delay line coupled to a source of microwave power, means at a substantially higher potential than said delay line for emitting electrons, means including crossed electric and magnetic fields for compelling said electrons to travel in energy exchanging relationship with microwaves propagated in said delay line thereby extracting energy from said waves and impinging upon said delay line, and a load coupled between said emitting means and said delay line whereby said microwave power is converted to DC. power in said load.

5. An electron discharge device comprising a slow wave propagating structure energized by a source of microwave signal and disposed adjacent an elongated space coextensive therewith, means injecting electrons into said interaction space, means producing crossed electric and magnetic fields in said space for compelling electrons to travel therethrough in energy exchanging relationship with microwaves propagated in said structure and a DO load coupled between said electron emitting means and said structure, whereby electrons enter said interaction space, proceed therethrough gaining energy from said wave and moving toward said structure as the electron energy increases and impinge upon said structure, thus providing a flow of electrons from said emitting means to said structure, increasing the DC. potential of said emitting means and converting microwave power from said source to DC. power in said load.

6. A microwave rectifier comprising a crossed-field traveling wave tube including a slow wave structure, an elongated electrode coextensive with said structure forming an interaction space therebetween and means emitting electrons at one end of said space; a source of microwave input power coupled to said structure; an output load coupled between said emitting means and said structure; and means applying potentials to said structure, said elongated electrode and said emitting whereby emitted electrons are compelled by said crossed fields to travel through said space at energy exchanging relationship with microwaves propagated in said structure so as to move toward and impinge upon said structure as said electrons gain energy from said wave thereby converting input microwave power to DC. power in said load.

7. A microwave rectifier comprising a crossed-field traveling wave device with potentials applied thereto for maintaining the delay line in said device negative with respect to other electrodes therein and a DC load coupled between the cathode and delay line in said device whereby microwave power applied to said delay line is converted to DC. power in said load.

8. A microwave rectifier comprising a crossed-field traveling wave device with potentials applied thereto for maintaining the delay line in said device negative with respect to the cathode therein and a DC. load coupled between the cathode and delay line in said device whereby microwave power applied to said delay line is converted to DC power in said load.

9. A microwave rectifier comprising a crossed-field traveling wave device with potentials applied thereto so that electrons flow from the cathode to the delay line in said device raising cathode potential above delay line potential therein and a DC. load coupled between said cathode and delay line whereby microwave power ap plied to said delay line is converted to DC. power in saidload.

References Cited by the Examiner UNITED STATES PATENTS 2,804,569 8/1957 Huber 3l5-3.5 X 2,892,957 6/1959 Waters 3153.5 X 2,957,983 10/1960 George 3153.5 X 3,090,925 5/1963 Adler et al. 3153.6

LLOYD MCCOLLUM, Primary Examiner.

ARTHUR GAUSS, GEORGE N. WESTBY, Examiners. 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING A SLOW WAVE PROPAGATING STRUCTURE BIASED AT A NEGATIVE D.C. POTENTIAL COUPLED TO A SOURCE OF ALTERNATING MICROWAVE FREQUENCY SIGNALS, MEANS EMITTING ELECTRONS AT A HIGHER NEGATIVE POTENTIAL THAN SAID SLOW WAVE STRUCTURE POTENTIAL, MEANS COMPELLING SAID ELECTRONS TO TRAVEL IN ENERGY EXCHANGING RELATIONSHIP WITH WAVES PROPAGATED IN SAID STRUCTURE AND A D.C. LOAD COUPLED BETWEEN SAID EMITTING MEANS AND SAID STRUCTURE WHEREBY POWER FROM SAID SOURCE OF ALTERNATING SIGNAL IS CONVERTED TO D.C. POWER APPLIED TO SAID LOAD. 